Cherry rootstock plant named ‘STO2’

ABSTRACT

A new and distinct cultivar of  Prunus  plant named ‘STO2,’ characterized by its weeping plant habit and typical slow growth; good adaptation at hot and dry conditions; and as a rootstock, slow vegetative growth that imparts uniformity, higher yield and better fertility to the grafted variety as compared to a standard rootstock such as Gisela 5, F12/1 and Mazzard.

Latin name of the genus and species: The Latin name of the genus and species of the plant variety disclosed herein is Prunus cerasus L.×P.×schmittii Rehder.

Variety denomination: The inventive cultivar of Prunus cerasus L.×P.×schmittii Rehder disclosed herein has been given the varietal denomination ‘STO2.’

BACKGROUND OF THE INVENTION

The present invention relates to a new and distinct cultivar of Prunus plant, typically used as a cherry tree rootstock, botanically known as Prunus cerasus L.×P.×schmittii Rehder, and hereinafter referred to by the name ‘STO2.’

The new and distinct variety of cherry hybrid tree of the present invention was bred as a cross of Prunus cerasus with a Prunus canescens hybrid (Prunus avium and Prunus canescens) in Germany in 1989. It has been successfully asexually propagated by tissue culture. The purpose of breeding program was to find a better adapted cherry rootstock. The new Prunus plant is better adapted on heat and aridity than other rootstocks with a slow vegetative growth. The breeder also succeeded in creating a new cherry rootstock, which has a higher yield and influences the grafted variety positively in fertility.

SUMMARY OF THE INVENTION

Plants of the new Prunus have not been observed under all possible environmental conditions. The phenotype may vary slightly with variations in environment such as temperature and light intensity without any variance in genotype.

The following traits have been repeatedly observed and are determined to be the unique characteristics of ‘STO2.’ These characteristics in combination distinguish ‘STO2,’ as a new and distinct cultivar of Prunus:

-   -   1. Weeping plant habit;     -   2. Good adaptation to hot and dry clime conditions;     -   3. As a rootstock, with slow vegetative growth, it produces a         dwarf tree;     -   4. As a rootstock, imparts uniformity and higher yield to the         grafted variety as compared to, for example, Gisela 5, F12/1 and         Mazzard;     -   5. As a rootstock, trees are around 70% slower than on Prunus         avium seedlings; that is, the trees, for which ‘STO2’ is used as         rootstock, grow more slowly and thus result in a dwarf tree that         is smaller than, for example, a Prunus avium seedling; and     -   6. Absence of suckers.

As used herein, “higher yield” refers to the impact of the rootstock of the tree on both vegetative as well as generative growth. Thus, the rootstock can affect the generative growth and assist the grafted species to achieve greater yield. Therefore, with regard to ‘STO2,’ the yield per tree and crown volume is higher than that of a standard rootstock such as Gisela 5, F12/1 and Mazzard.

Further with ‘STO2’ as the rootstock, the grafted variety can achieve better fertility (i.e., greater generative growth). That is, use of ‘STO2’ as a rootstock results in greater generative growth than in the case of standard rootstock (Gisela 5, F12/1, Mazzard); the tree produces more flowers, more fruit, with a greater yield of the same or larger fruit size. In the end greater output is achieved.

The parents of ‘STO2’ are partly a hybrid between Prunus avium and Prunus canescens (unnamed and not patented) and the other part a Prunus cerasus wild species (unnamed and not patented). The parent (Prunus avium×Prunus canescens) is known for stronger growth than the new hybrid (STO2). The parent (Prunus avium×Prunus canescens) grows perpendicularly, while the new cultivar (‘STO2’) grows pendulously. Further, the parent Prunus cerasus is known for a distinctly more rounded leaf than the new hybrid (STO2). Leaf of STO2: narrow and elongated, Leaf of parent Prunus cerasus: round.

Plants of the new Prunus, ‘STO2’, also can be compared to plants of Prunus ‘GI 2091’ (U.S. Plant Pat. No. 16,173, issued Dec. 27, 2005). In side-by-side comparisons conducted in Kressbronn, Germany, plants of the new Prunus differed primarily from plants of ‘GI 2091’ in the following characteristics:

-   -   1. As a rootstock, plants of the new Prunus have about 10%         stronger growth (i.e., faster growth) in comparison to plants         with ‘GI 2091’ rootstocks;     -   2. Plants of the new Prunus do not develop stipules, whereas ‘GI         2091’ plants develops stipules;     -   3. Plants of the new Prunus have a weeping habit, whereas ‘GI         2091’ plants have an upright habit; and     -   4. Due to its typical/characteristic growth, plants of the new         Prunus impart higher yield to the scion plant than plants of ‘GI         2091.’

‘STO2’ was first asexually propagated in autumn of 2001 in Freising, Germany, using tissue culture. Asexual reproduction of Prunus rootstock plant ‘STO2’ by tissue culture since autumn 2001 has shown that the unique features of this new variety are stable and the plant reproduces true to type in succeeding generations of asexual reproduction.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying photographs illustrate the overall appearance of the new Prunus plant. These photographs show the colors as true as it is reasonably possible to obtain in colored reproductions of this type. Colors in the photographs may differ slightly from the color values cited in the detailed botanical description which accurately describe the colors of the new Prunus plant.

FIG. 1 provides a side perspective view of a typical tree of ‘STO2’ grown in an outdoor orchard.

FIG. 2 provides a close-up view of leaves of a tree of ‘STO2.’

FIG. 3 provides a close-up view of fruits, branches and leaves of ‘STO2.’

DETAILED BOTANICAL DESCRIPTION

The aforementioned photographs, following observations and measurements describe plants grown during the summer in Kessbronn, Germany in an outdoor orchard and under conditions and practices generally used in commercial cherry production. Plants were 12 years old when the photographs and descriptions were taken. Measurements and numerical values represent averages for typical plants and plant parts. The actual measurements of any individual plant or plant parts, or any group of plants or plant parts, of the new Prunus plant may vary from the stated average. In the following description, color references are made to The Royal Horticultural Society (R.H.S.) Colour Chart, except where general terms of ordinary dictionary significance are used.

‘STO2’ has a generally arched plant habit and is slow in growth. The weeping plant habit is typical for the new Prunus plant. After twelve growing seasons in Kressbronn, Germany, a height of about 3.7 meters, a width of about 2.95 meters and a trunk diameter of about 9.3 cm were observed for ‘STO2.’ The growth reduction induced by ‘STO2’ allows a highly intensive cherry production with dwarf trees.

-   Botanical classification: Prunus cerasus L.×P.×schmittii Rehder     ‘STO2.’ -   Parentage: Breeding between Prunus cerasus and a Prunus canescens     hybrid. -   Propagation:     -   -   Type.—By asexual reproduction.         -   Method.—By tissue culture since the autumn of 2001 in a             controlled environment. The process is similar to the             propagation of other cherry rootstock. -   Plant description:     -   -   Plant use.—Only as a rootstock.         -   Plant form.—Semi-ellipsoid form, after 3 years reflexed             branching.         -   Plant and growth habit.—Weeping plant habit; plant are             typically grown as a single stem; weak vigor (i.e., slow             growth).         -   Stem description.—Strength: Strong. Texture: Rough. Color:             Grey brownish RHS 199B.         -   Leaf description, fully developed leaves.—Arrangement:             Alternate; simple. Length: About 8 cm to about 9.5 cm.             Width: About 3.7 cm to about 4.5 cm. Shape: ovate, very             elongated. Apex: Acute. Tip: Acuminate. Base: Obtuse,             convex. Margin: Biserrate. Texture, upper surface: Glabrous.             Texture, lower surface: Coarse, pubescent. Color: Fully             developed leaves, Upper surface: Close to RHS 141B;             Venation: Close to RHS 146C. Fully developed leaves, Lower             surface: Close to 144A; Venation, Close to RHS 144C.         -   Petiole description.—Length: About 1.3 cm to about 1.9 cm.             Diameter: About 0.2 cm. Color, upper surfaces and lower             surfaces: Close to RHS161A.         -   Presence of stipules.—Absent. -   Flower description:     -   -   Flower type/habit.—3 to 6 flowers single flowers arranged             one compound panicles. Flowers occur in general on one year             old branches.         -   Fragrance.—Weak, pleasant.         -   Natural flowering season.—In April, in south Germany,             flowering occurs at about the same time as ‘GI 2091,’             patented cherry rootstock (U.S. Plant Pat. No. 16,173).         -   Lastingness of entire bloom period.—About 15 days.         -   Lastingness of an individual bloom.—About 8 days.         -   Inflorescence height.—About 3.5 cm to about 4 cm.         -   Inflorescence diameter.—About 2.5 cm to about 3.5 cm.         -   Flower diameter.—About 1.4 cm to about 1.8 cm.         -   Flower depth.—About 0.8 cm to about 1.1 cm.         -   Bud length.—4-8 mm.         -   Bud width (bud diameter).—2-3 mm.         -   Bud shape.—Cylindrical, acutely pointed at the projecting             ends.         -   Bud colour.—Brown to light brown-RHS-165A.         -   Bloom quantity.—Fertile, a large quantity of flowers occur             each year. Remarkably, the flowers occur on only the one             year old branches.         -   Petals.—Arrangement: Five petals in a single whorl. Slightly             overlapping. Length: About 0.5 cm to about 0.9 cm. Width:             About 0.5 cm to about 0.7 cm. Shape: Oblong, slightly             elongated. Apex: Rounded, slightly elongated. Base:             Truncate. Margin: Entire. Texture, upper and lower surfaces:             Smooth, glabrous. Color: When fully opened, upper surface:             Close to RHS 155B. When opening and fully opened, lower             surface: Close to RHS 155B.         -   Sepals.—Arrangement: Five sepals in a single whorl. Length:             About 0.3 cm. Width: About 0.11 cm to about 0.23 cm. Shape:             Angular set, triangular, slightly elongated. Apex: Pointed.             Base: Truncate. Margin: Entire. Texture, upper and lower             surfaces: Smooth, glabrous. Color, upper surfaces: Close to             RHS 142B. Color, lower surfaces: Close to RHS 145B.         -   Pedicels.—Length: About 1.5 cm to about 1.9 cm. Diameter:             About 0.1 cm. Angle: About semi-erect to semi-prostrate from             the inflorescence stalk. Texture: Smooth, glabrous. Color:             Close to RHS 142A.         -   Peduncle.—Length: About 0.2 cm to about 1.1 cm. Diameter:             About 0.2 cm. Surface: Smooth. Color: Close to RHS 149A.         -   Reproductive organs.—Stamens: Quantity per flower: Numerous.             Filament length: About 4 mm to about 7 mm. Filament color:             Close to RHS 155B. Anther length: About 0.3 mm to about             0.8 mm. Anther color: Close to RHS 6A. Pistils: Quantity per             flower: One. Pistil length: About 8 mm to about 13 mm. Style             length: About 6 mm to about 11 mm. Style color: Close to RHS             150C. Stigma shape: Round. Stigma color: Close to RHS 150A.         -   Fruit description.—Maturity when described. Date picking:             July in south Germany, varies with climatic conditions.             About the same time as ‘GI 2091,’ patented cherry rootstock             (U.S. Plant Pat. No. 16,173). Size: very small to small             about 1 cm to about 1.3 cm diameter. Average weight: 1.2 g,             varies slightly with fertility of the soil, amount of             thinning and climatic conditions. Form: Globose, Slightly             flat at the apex. Stem cavity: Slightly obcordate to flat.             Color: RHS 185A.         -   Peduncle description.—Size: Average length about 3.4 cm.             Average diameter about 0.09 cm. Color: RHS 149A.         -   Stone description.—Average length: About 0.74 cm. Average             width: About 0.6 cm. Average thickness: 0.55 cm. Form:             Nearly globose. Base: round. Apex: Rounded. Color: RHS 163C             when dry.         -   Fruit use.—Not to be used as a dessert fruit. -   Pollination requirements: ‘STO2’ is not self-fertile and requires a     pollinator. -   Temperature tolerance: Plants of the new Prunus have been observed     to tolerate temperatures from about −20° C. to about 40° C. Notably,     under hot and dry climate climatic conditions, ‘STO2’ trees do not     exhibit chlorosis. These trees are very robust in the presence of     substantial variations in temperature (very low temperatures in     winter (−20° C.) and very hot temperatures in summer (+40° C.)) and     such temperature fluctuations have no negative effect on the trees. -   Drought tolerance: Due to a deep root system, the ‘STO2’ variety is     tolerant to drought conditions. 

What is claimed is:
 1. A new and distinct cultivar of Prunus cerasus L.×P.×schmittii Rehder plant named ‘STO2,’ substantially as illustrated and described herein. 